This invention relates generally to blow molding machines and, more particularly, to shuttle blow molding machines that utilize a continuous parison extruder head.
Blow molding machines of the type contemplated herein utilize a number of mold units that are moved sequentially through different workstations for such operations as label insertion, receiving a charge of parison, pressurized expansion of the parison within the mold, and removal of the cured article prior to another cycle of these operations. In a shuttle machine, the mold units are transferred between the different workstations using an indexing mechanism that provides either simple linear or compound translation of the mold units from one workstation to the next.
Various different sequencing approaches have been proposed over the years. See, for example, U.S. Pat. No. 3,998,576 to Frohn et al. in which each of a number of mold units are shifted along an inclined path first upwardly under an extruder head and then downwardly away from the extruder head, with the mold unit then being shifted laterally to make room for an adjacent mold unit to shift over so that it may then move into and out of position under the extruder head. U.S. Pat. No. 5,576,034 to Kiefer et al. discloses a shuttle-type machine in which mold units are shuttled along a path to a location under a takeout mechanism where they are opened for article removal. Thereafter, they are pivoted or otherwise shifted laterally underneath an extruder head to receive parison, then closed and shifted back in place and shuttled to the next position.
In high production capacity blow molding machines, maximizing the output rate of the machine requires a design that minimizes the dwell time at each station and the indexing time between stations. However, there are additional considerations as well. For example, although the cure time for a blown article can be controlled to some extent by cooling of the mold, there is a minimum amount of time necessary before the article is sufficiently cured to be removed from the mold. In high production machines, this minimum cure time can be problematic, as the cure time may be ten times (or more) longer than the amount of time for the slowest of the workstations to carry out its operation. One way to accommodate this cure time is to increase the total indexing period (that is, the period of time that elapses between indexing steps) to slow down the machine to a rate that provides enough cure time before reaching the takeout station. A disadvantage of this approach is that it artificially reduces the throughput rate of the machine from what it could otherwise accomplish. Another solution is to increase the number of mold units to a large enough number that by the time any one mold unit has cycled through back to the takeout station, the article has had sufficient time to cure even though the machine is running as fast as its slowest workstation and the indexing mechanism allows. Such an approach may involve using twelve or more mold units on a single machine, in which case the actual layout and sequencing of the mold units can have a considerable impact on, for example, the total area required for the machine.
The present invention is directed to a shuttle blow molding machine in which two groups of mold units are located on opposite sides of a series of workstations spaced along a horizontal workstation path, with the mold units each including a mold that can advance from a retracted position that is offset from the workstation path to an extended position that is aligned with the workstation path. The blow molding machine includes an extruder head and a takeout mechanism both located along the workstation path. Each of the mold units has, in addition to the mold, a carriage, clamp, and blow pin assembly. The mold includes a pair of mold halves located in the clamp with the mold being movable by the clamp between an open position, in which the mold halves are spaced from each other, and a closed position, in which the mold halves are mated together to define one or more mold cavities. The blow pin assembly is supported by the clamp and includes at least one blow pin that is movable between a retracted position away from the mold and an inserted position in which the blow pin is located within a corresponding hole in the mold to deliver pressurized gas to the corresponding mold cavity. The clamp is mounted on the carriage with the carriage being movable in a direction transverse to the horizontal workstation path such that the mold can reciprocate between the retracted and extended positions. The mold units within the first group are located in side-by-side relation adjacent each other and are movable as a group along a first path that is parallel to the workstation path. Similarly, the mold units within the second group are located in side-by-side relation adjacent each other and are movable as a group along a second path that is parallel to the workstation path. Each group can be indexed along its parallel path to successively pass each mold within the group through the various workstations. The transverse motion of the molds between their retracted and extended positions allows one group to be retracted out of the way while the other group advances through the workstations.
In accordance with another aspect of the invention, there is provided a shuttle blow molding machine which implements a sequencing process in which two groups of mold units are alternately indexed past a number of workstations in a cyclical fashion. As mentioned above, the machine includes an extruder head and takeout mechanism located along a workstation path, with first and second groups of mold units located on opposite sides of the workstation path and each having a mold that can move in a direction transverse to the workstation path between a retracted and extended position. The machine further includes first and second indexers connected to the first and second groups of mold units, respectively, with each of the indexers being operable to move its associated group of mold units together along a path that is parallel to the workstation path. The machine also includes a controller connected to the mold units and indexers. The controller is operable to advance the mold units through repetitive cycles in which the mold units of the first and second groups are indexed in a forward direction along their respective paths from a starting position, through the takeout mechanism and extruder head stations, to a end position, and then are moved in a return direction along their respective paths from the end position back to the starting position. When the mold units are moving in the forward direction, the molds are moved from their retracted position toward their extended position prior to entering the takeout station and then are moved back to their retracted position after leaving the extruder head. The mold units of the first group are indexed together sequentially through the stations followed by the mold units of the second group which are indexed together sequentially through the stations while the mold units of the first group return to their starting position.
In accordance with another aspect of the invention, there is provided a shuttle blow molding machine having a number m of adjacent workstations spaced along a horizontal workstation path and first and second groups of mold units, each group having a number n of adjacent mold units. The two groups of mold units are located on opposite sides of the workstation path and, as above, each of the mold units includes a mold that is movable in a direction transverse to the workstation path such that the mold can reciprocate between a retracted position, in which the mold is spaced from the workstation path, and an extended position, in which the mold is centered along the workstation path. Each group of mold units indexes along a path parallel to the workstation path among at least 2(nxe2x88x921)+m index positions. Preferably, there are at least 2n+m index positions.
The mold units of each group can have individual bases that are connected together to form a tram that is moved as a single unit along its parallel path. The bases can be connected together in a manner that permits the addition or removal of mold units, as well as adjustments to the center distances between the mold units. The relative positioning of the workstations can also be adjusted to match these center distances.